U.S. Pat. No. 5,108,037 describes swirl-producing fuel injectors in which two flow paths are formed for the fuel. The fuel flow is split into two components in the area of the valve closing body. One component of the fuel flows through swirl channels arranged in a swirl disk. The fuel flow is imparted at a circumferential velocity which results in fuel being spray-discharged onto a conical envelope. The swirl disk has a central bore which is used to guide the valve closing body. The gap formed between the guide bore and the valve closing body is utilized in a targeted manner to permit a fuel leakage flow which flows without swirl in the axial direction through the guide bore. Upstream from the sealing seat, the axial fuel flow encounters the fuel flow in which a swirl has been induced. The fuel flows combine and are spray-discharged jointly. Therefore, fuel may be spray-discharged not only on a conical envelope but also as a solid cone.
German Patent Application No. 198 15 795 Al also describes a fuel injector in which two flow paths are formed to create a biflux flow. These flow paths are created in a common component which is inserted downstream from the sealing seat. This component is manufactured in a multilayer process and is inserted into a recess on the downstream end of the fuel injector. The fuel jet is spray-discharged directly out of the component that produces the swirl. The fuel flow is divided in this component into an axial flow component and a swirling flow component. The axial component of the flow is sent eccentrically to the swirling fuel flow again, so that the cone on which the fuel is spray-discharged becomes inclined toward the central axis of the fuel injector.
In the case of the fuel injector described in U.S. Pat. No. 5,108,037, the increased tolerance between the valve closing body and the guide bore is a disadvantage. This is necessary to achieve an adequate leakage flow to produce an axial flow. Due to the use of a spherical valve closing body and the associated linear throttling point, unavoidable fluctuations in fit are associated with a great scattering in the axial flow component. This increases the reject rate in manufacturing the fuel injector.
Another disadvantage is the inferior guidance of the valve closing body due to the greater radial clearance between the valve closing body and the guide bore. The valve closing body has fuel flowing around it during the spray-discharging process. Due to the spherical geometry and the increased clearance between the valve closing body and the guide bore, the tendency to vibrate is increased. Flutter of the valve closing body in turn results in greater wear on the fuel injector.
In the case of the fuel injector described in German Patent Application No. 198 15 795 Al, however, the arrangement downstream from the sealing seat is a disadvantage. This may easily produce carbonization of the swirl-producing component. It is therefore impossible to ensure reliable and constant processing of the fuel to be spray-discharged. Consequently, the atomization is inferior and ultimately there is an increased pollution burden due to the inferior combustion.
The fuel flow is split and then recombined downstream from the sealing seat. Therefore, there cannot be any change in the axial component of fuel flow during opening and closing of the valve.
The swirl element, which is constructed in multiple layers, also requires a complex manufacturing process and must be inserted into the fuel injector in the correct orientation due to the asymmetrical arrangement of the axial flow channel. This increases the manufacturing costs of the fuel injector.